The present invention relates to the determination of conditions in centrifuged blood using measured pressure in an aspirate or dispense process. In particular, the present invention relates to detecting or confirming the aspiration of packed red blood cells from centrifuged blood.
Most blood donations are divided (fractionated) into their components: red blood cells, platelets, clotting factors, plasma, antibodies (immunoglobulins), and white blood cells. Depending on the situation, people may receive only the cells from blood, only the clotting factors from blood, or some other blood component. Transfusing only selected blood components allows the treatment to be specific, reduces the risks of side effects, and can efficiently use the different components from a single unit of blood to treat several people.
Packed red blood cells (PRBC), the most commonly transfused blood component, can restore the blood's oxygen-carrying capacity. This component may be given to a person who is bleeding or who has severe anemia. The red blood cells are separated from the fluid component of the blood (plasma) and from the other cellular and cell-like components. This step concentrates the red blood cells so that they occupy less space, thus the term “packed.” Red blood cells can be refrigerated for up to 42 days. In special circumstances—for instance, to preserve a rare type of blood—red blood cells can be frozen for up to 10 years. Thus, the ability to separate PRBCs from other components for transfusion is important.
The field of immunohematology is the science of antigens and antibodies as they relate to the management of transfusion by donor and transfusion services. Applications of immunohematology include the definition of blood types, and the identification of unexpected antibodies that may lead to incompatible transfusions and transplants or complications during pregnancy. Both recipient (patient) and donor blood is tested to assure a safe blood transfusion.
Blood typing may be carried out manually or on automated or semi-automated systems such as the ORTHO PROVUE® sold by Ortho-Clinical Diagnostics, Inc.
In immunohematology as well as clinical chemistry, whole blood must sometimes be spun down into layers of its various components by centrifugation before it can be analyzed. The layers are mainly composed of plasma, a buffy coat which contains white blood cells and plasma, and packed red blood cells (PRBC).
Packed red blood cells are important for a variety of reasons in addition to those listed. PRBCs are needed to in order to do some of the types of testing in immunohematology. The PRBCs are used in a diluted form typically in a dilution ratio of 0.8% and 4.0% to the appropriate manufactured saline diluent. To aspirate the PRBCs, the metering probe must go through the plasma layer of the centrifuged blood.
Thus, from both a transfusion and immunohematology perspective, it is important to be able to identify and separate out PRBCs from the other components of blood. Known methods for identifying and separating PRBCs from other components of blood have included operator observations prior to testing (e.g., blood typing) or using an imaging system post testing. Such post testing suffers from lack of accuracy and the need to rerun a test if separation was incomplete or if the wrong layer was aspirated. It is also important from both a transfusion and immunohematology perspective to be able to detect other conditions in centrifuged blood, such as an error condition of incomplete centrifugation, or other error conditions.
There is still a need to be able to distinguish between various layers of blood components, such as a layer of PBRCs from other components of blood after centrifugation and to determine other conditions that may be present in centrifuged blood samples.